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| United States Patent |
5,024,875
|
|
Hill
, et al.
|
June 18, 1991
|
Antimicrobial microporous coating
Abstract
Waterproof, moisture-vapor-permeable urethane-coated fabrics with durable
antimicrobial properties that remain after repeated launderings are
prepared by incorporating bioactive silyl quaternary ammonium salts into
the polyurethane elastomer solvent solution that forms a microporous
polyurethane layer by the wet coagulation method on a base fabric.
| Inventors:
|
Hill; Berlie R. (Cana, VA);
Watson, Sr.; Thomas F. (Greensboro, NC);
Triplett; Benny L. (Pleasant Garden, NC)
|
| Assignee:
|
Burlington Industries, Inc. (Greensboro, NC)
|
| Appl. No.:
|
905135 |
| Filed:
|
September 9, 1986 |
| Current U.S. Class: |
442/77; 427/246; 427/354; 428/315.5; 428/423.5; 428/907; 442/124; 523/122 |
| Intern'l Class: |
B05D 003/10; B32B 005/18; B32B 005/20 |
| Field of Search: |
427/246,354
428/315.5,423.5,907,267
523/122
|
References Cited
U.S. Patent Documents
| 3968292 | Jul., 1976 | Pearman et al.
| |
| 4024307 | Mar., 1977 | Brahm et al.
| |
| 4028451 | Jun., 1977 | Warwicker.
| |
| 4370981 | Feb., 1983 | Sanderson.
| |
| 4429000 | Jan., 1984 | Naka et al.
| |
| 4460369 | Jul., 1984 | Seymour.
| |
| 4504541 | Mar., 1985 | Yasuda et al.
| |
| 4507413 | Mar., 1985 | Thoma et al.
| |
| 4554198 | Nov., 1985 | von Blucher et al.
| |
| Foreign Patent Documents |
| 2367606 | May., 1978 | FR.
| |
| 1597143 | Sep., 1981 | GB.
| |
| 2059872 | Sep., 1981 | GB.
| |
Other References
"Recent Developments in Coated Apparel", by Robert Lomax, pp. 91-99,
Journal of Coated Fabrics, vol. 14, Oct. 1984.
"The Mechanism and Prevention of Microbial Attack on Polyurethane
Coatings", by Dr. B. F. Sagar, Shirley Institute, Publ. S.41, 71-83,
(1981).
Derwent Abstract of Published French application 7631247.
"Defensive Publication", published Aug. 1, 1972.
International Dyer & Textile Printer, article entitled, "Actifreshtreated
Polyurethane", Jan. 6, 1978, p. 36.
Textile World, article entitled, "High-Performance Coatings and Finishes
Expand Uses", May 1985, by Richard Mansfield, pp. 58-60.
PCT International Search Report.
Bayer Pocket Book for the Plastics Industry, 3rd Edition, pp. 63-119,
(1963).
|
Primary Examiner: Cannon; James O.
Attorney, Agent or Firm: Nixon & Vanderhye
Claims
What is claimed is:
1. A process of making a waterproof, water-vapor-permeable, antimicrobial
coated fabric having a durable, antimicrobial, microporous polyurethane
layer thereon formed by the wet coagulation method, said process
comprising applying a water-miscible, polar organic solvent solution of a
polyurethane elastomer to a base fabric, immersing the thus-coated base
fabric into an aqueous coagulation bath to extract the solvent from the
polymer solution leaving a porous polyurethane matrix adhered to the base
fabric, then washing and drying the coated fabric, wherein the
polyurethane elastomer solution contains a bioactive amount of a bioactive
silyl quaternary ammonium compound of the formula:
##STR2##
wherein R is an alkyl of 11 to 22 carbon atoms and R.sup.1 is bromine or
chlorine, the resulting coated fabric having a moisture vapor transmission
of at least 800 g/m.sup.2 /24 hours and a hydrostatic pressure resistance
of at least 10 psi.
2. The process of claim 1 in which from about 0.01 to about 10 weight
percent of the bioactive compound is present in the solution.
3. The process of claim 2 in which from about 0.08 to about 4.0 weight
percent of the bioactive compound is present in the solution.
4. A waterproof, water-vapor-permeable, antimicrobial coated fabric
resistant to the spread of mildew, produced by the process of claim 1.
5. A process of preparing a polyurethane-based coating solution for
application to a fabric substrate to form a rainproof,
water-vapor-permeable coated fabric with durable antimicrobial properties,
a moisture-vapor transmission of at least 800 g/m.sup.2 /24 hours, and a
hydrostatic pressure resistance of at least 10 psi, said process
comprising the sequential steps of:
(a) mixing together a methanol solution of a bioactive silyl quaternary
ammonium compound of the formula:
##STR3##
wherein R is an alkyl of 11 to 22 carbon atoms and R.sup.1 is bromine or
chlorine, with N,N-dimethylformamide and a surfactant to form a first
solution;
(b) preparing a solution of at least one polyurethane resin in a
water-miscible, compatible liquid vehicle; and
(c) combining the solutions of steps (a) and (b) to form a
water-coagulable, polyurethane-based, bioactive coating composition for
application to fabric substrates via the wet coagulation method to make
microporous, rainproof, water vapor-permeable antimicrobial coated fabrics
resistant to the spread of mildew.
6. The product produced by the process of claim 5, wherein the durable
antimicrobial properties are characterized by a retention of at least 50%
of the original bioactivity after 10 launderings.
Description
BACKGROUND OF THE INVENTION
This invention relates to a moisture-permeable waterproof coated fabric.
More particularly, it is concerned with a moisture-permeable waterproof
fabric having an antimicrobial microporous polymeric coating thereon, the
fabric having good moisture-permeability with durable waterproofness and
antimicrobial properties that remain characteristic of the fabric even
following multiple launderings. Procedures for making such fabrics are
also described.
Coated fabrics suitable for use as rainwear function by blocking the pores
of a woven, knitted or non-woven fabric with a cohesive polymer film which
acts as a physical barrier against wind, water, and in the case of
protective workwear, aggressive chemicals, oils, and greases. This barrier
or coating distinguishes polymer coatings from chemical finishes which
merely coat the individual fibers of a fabric without blocking the pores,
and repel fluids by surface tension effects. Polymeric coatings have been
based upon, initially rubber or synthetic or fluorocarbon rubbers, and
more recently, polyurethanes, acrylics, silicone elastomers and
polyvinylchlorides.
Fashion and leisurewear, particularly rainwear, require that the coated
material is attractive with good drape and handle, be water repellent,
although not necessarily for prolonged use in heavy rain, and that the
fabric retain these properties after dry cleaning or laundering. There are
several fabrics available that satisfy the conflicting requirements of
waterproofness and breathability. One example is the laminated fabric
known as Gore-Tex (W. L. Gore and Associates) which transmits perspiration
through a microporous polytetrafluoroethylene (PTFE) film which is
laminated between, usually, a woven nylon outer and a tricot inner fabric
with a discontinuously applied adhesive. Another similarly qualified
fabric, in the sense of waterproofness and breathability, is Entrant,
which is a woven nylon fabric coated with a microporous polyurethane film
formed by the so-called wet coagulation technique as in U.S. Pat. No.
4,429,000 to Toray Industries, Inc. Other polyurethane coated fabrics are
described in U.S. Pat. No. 3,360,394 to Griffin. In the wet coagulation
method a thin, microporous polyurethane layer is formed on a base fabric
by applying a coating solution of a polyurethane dissolved in a polar
organic solvent that will solubilize the polyurethane yet is miscible with
water. The polymer solution is applied to the fabric substrate by knife
coating or the like, then immersed in a bath of water which selectively
dissolves or mixes with the organic solvent, exchanges water for the polar
solvent and causes the previously dissolved polyurethane to coagulate
leaving a thin, microporous coating having a cellular substructure on the
fabric. Surface pores are generally one micron or less in diameter. Such
pores are small enough to exclude water droplets and yet they provide a
tortuous physical pathway from the base fabric to the coating surface,
leading to a water-vapor-permeable fabric.
Rain-soaked and badly soiled garments must be cleaned or at least dried
before long term storage to prevent proliferation of airborne bacteria and
fungal spores that find a warm, moist environment hospitable. Such
organisms find the cellular structure of this type of fabric attractive
and can attack certain synthetic polymers, causing degradation of the
polymer, in some cases, or at least permanent discoloration. Lomax, in the
1984 survey article Recent Developments in Coated Apparel, Journal of
Coated Fabrics, Vol 14, October 1984, reports that natural rubber and some
grades of PVC and polyurethane coatings have been protected by
incorporated bacterocides and fungicides. In susceptible polymer coatings,
biodegradation may be initiated in microscopic cracks and can eventually
lead to delamination of the coating from the fabric and consequent loss of
waterproofness.
The cellular structure of this type of microporous coating is subject to
contamination with body oils, particularly when used as an article of
apparel, due to direct contact with the skin or indirect transmission
through a lining fabric. Thus, the potential exists for the production of
undesirable odors, mildew and even discoloration since all the ingredients
needed are present, namely, moisture, heat, and a nutrient for bacteria.
It is also known that organic polymers are subject to bacterial attack
which can result in deterioration of the polymer. A real need exists for
the prevention of these undesirable occurrences.
The microporous coating of the present invention imparts to a microporous
coated fabric the ability to prevent odor, discoloration, mildew, even
discoloration due to bacterial growth. Furthermore, the coating retains
its effectiveness even following repeated launderings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of one arrangement for coating a fabric with an
antimicrobial, moisture-permeable, water-repellant layer of polyurethane.
DETAILED DESCRIPTION OF THE INVENTION
It is well known that topical application of antimicrobial agents to
textile fabrics, i.e. fabric finishes, can provide some degree of
protection against bacterial growth. Most of these agents show a reduction
of bacterial growth in a culture media when a treated fabric is immersed.
The mechanism of bacterial reduction is by activity of the antimicrobial
in solution, and this means that the antimicrobial must leach out from the
treated fabric to be effective. To be effective, leaching is required, and
when leaching occurs, the durability of the treatment must be finite
since, eventually, it will become depleted.
It is also known that certain antimicrobial agents have the ability to
chemically bond to fibers and retain their effectiveness over a long
period of use One of these antimicrobial agents is
3-(trimethoxysilyl)-1-propyloctadecyldimethylammonium chloride, produced
by Dow Corning Corporation and marketed under the name of DC-5700.
Initially, a topical application of this material to a microporous coated
fabric provided a durable, bacteriostatic product. This approach was tried
with good results. However, since various types of fabrics that are coated
require different amounts of coating to achieve desired properties, and in
some cases this coating can be relatively thick, it was not known whether
the topical treatment effectively permeated the entire coating. For these
reasons it appeared that the most effective way to insure completeness of
treatment with the antimicrobial agent would be to include it in the
coating itself. Unfortunately, the improved bioactive compound is
furnished by the supplier as a solution in methanol, which is not a
solvent for polyurethane, the polymer used in many microporous coatings.
Being a non-solvent, the methanol coagulated the polyurethane polymer when
the bioactive compound, with its methanol solvent, was added to the
coating solution. However, it was found by careful and proper technique
that the bioactive compound could be first dissolved in
N,N-dimethylformamide (DMF), a solvent for polyurethanes, and then
incorporated into the coating solution. By first solving this
coagulation/addition problem, it was then possible to produce a
coagulated, microporous coating having an antimicrobial agent throughout
the entire cellular matrix which would give maximum protection against
bacterial growth, coupled with maximum durability. The result is that not
only is the coating protected from undesirable bacterial growth but the
fabric, being in such close proximity to the now bacteriostatic coating,
is also rendered bacteriostatic. This finding does not preclude the
possibilities in some cases of an additional treatment of the fabric
itself either as a posttreatment finish or a pretreatment prior to
coagulation, or treatment of the combined fabric and coating with the
bioactive compound if a need arises. In fact, a treatment of coated fabric
with the bioactive compound is effective; however, with the discovery of
the ability to include the bioactive compound not merely on but in the
coating a more complete and effective protection is provided.
An additional and unexpected benefit of the addition of the bioactive
compound to the coating was that a softer product with better drape and
hand was obtained as compared to the same coating applied to a fabric
without the addition of the bioactive compound.
The coagulation process requires the water in the coagulation bath to
exchange with the solvent in the coating solution, as explained above.
Because methanol, as in the commercially available DC-5700, is completely
water soluble, it was expected that this would influence the substantivity
of the bioactive compound, i.e., that the bioactive compound would also be
exchanged and removed with the coating solvent. Surprisingly, it has been
discovered that the bioactive compound is actively bound to the coagulated
microporous coating since the water coagulation bath following coating and
coagulation, on analysis, did not reveal the presence of any bioactive
compounds. This is substantiated by the results of multiple home
launderings; while some loss of the bioactive compound occurs, the coated
fabric remains bioactive. Even after 10 machine washings, bacterial growth
is prevented, as explained in more detail in the evidence below.
The preferred bioactive, antimicrobial component of the coating composition
is a member of the class of
3-(trimethoxysilyl)-1-propyloctadecyldimethylammonium chloride which is
described in U.S. Pat. No. 3,730,701, the disclosure of which is hereby
incorporated by reference. A class of suitable bioactive silyl quaternary
ammonium compounds has the formula:
##STR1##
in which R is a C.sub.11-22 alkyl group and R.sup.1 is chlorine or
bromine. The preferred silyl quaternary ammonium salt
3-(trismethoxysilyl)-1-propyloctadecyldimethylammonium chloride chloride
and is available as a 42% active solids solution in methanol from Dow
Corning Corporation of Midland, Mich., under the designation DC-5700. This
material is well accepted in commerce and has the necessary U.S.
regulatory approvals, not only as a bacteriostatic textile treatment, but
also as a bactericidal component for medical device/non-drug applications.
The amount of the silyl quaternary ammonium bioactive material will be
within the following limits the minimum amount is the quantity needed to
achieve a specific minimum level of bioactivity, or to allow for process
variations, if any, to maintain a specific predetermined level. The
maximum amount will be limited by loss of substantivity on or in &he
coating as evidenced by excessive wash- or leach-out during laundering or
in use, or otherwise, and is balanced by the cost of this relatively
expensive component. Best results are obtained when the silyl quaternary
ammonium salt is present in an amount of from 0.01 to 10% by weight,
calculated on the weight in the coating mix, and preferably in the range
of 0.08% to 4% by weight similarly calculated.
Disclosed is a process for preparing a waterproof, water-vapor-permeable
antimicrobial coated fabric, exhibiting a good hydrostatic pressure
resistance, formed in a rapid and reproducible manner by coagulation from
a solvent solution of a polyurethane elastomer. The fabric is coated using
the wet coagulation method in which a polymeric elastomer, or mixture of
polymeric elastomers, is dissolved in a water-miscible polar organic
solvent. The polymer solution, to which a bioactive agent is added, is
coated onto a base fabric and then immersed in a coagulation water bath.
The water extracts the polar organic solvent, which is itself
water-miscible, from the coating, leaving a porous, spongy polyurethane
matrix having the specified porosity and other properties, on the base
fabric. Washing to remove any unextracted polar organic solvent and drying
follow. Optionally, a water repellent fluorocarbon finish is later
applied. A convenient thickener system based on acrylic acid polymers that
are compatible with the solvent/polyurethane system and soluble in the
solvent may be used to control and adjust coating solution viscosity
which, in turn, leads to thin, flexible polyurethane elastomer coatings
having the optimum performance and customer acceptance properties. The
thickener system is described in detail in copending, commonly assigned
application Ser. No. 903,130 filed Sept. 3, 1986, now U.S. Pat. No.
4,707,400 the disclosure of which is hereby incorporated by reference.
The coating solutions of the present invention are based upon urethane
resins dissolved in a water-miscible, polar solvent. A preferred series of
polyurethane resins are Texthane 620C and 420C available from Morton
Chemical division of Morton Thiokol. These are aromatic polyester urethane
resins, 620C characterized as a soft resin and 420C as a firm resin; both
are sold as DMF solutions whose physical and performance properties are as
follows:
______________________________________
620C 420C
______________________________________
Dry Content (%) 30 35
Viscosity (max) cps.
80,000 150,000
Solvent DMF DMF
Tensile strength (kg/cm.sup.2)
600 600
100% Modulus (kg/cm.sup.2)
80 100
Elongation (%) 550 400
______________________________________
Other components of the coating compositions
include nonionic surfactants, such as the Pluronic polyols, which are
surface active materials manufactured by BASF-Wyandotte and are block
copolymers of propylene oxide and ethylene oxide. The polyoxypropylene
serves as hydrophobe and the polyoxyethylene as lipophobe. As with the
acrylic acid component, a mixture of two of these nonionic surfactant
groups gives the best results. Average molecular weight for the Pluronic
L-35 is 1900, with polyoxypropylene equal to 50 weight percent. Pluronic
F-68 has an average molecular weight of 8350 with the polyoxypropylene
equal to 20 weight percent.
The water-miscible polar organic solvent of choice is
N,N-dimethylformamide, commonly referred to as DMF (CAS registry number
68-12-2), although other compatible solvents such as dimethylacetamide or
dimethylsulfoxide may be considered.
An amine is preferably added to neutralize the polyacrylic acid resin and
several amines may be useful; however, best results were obtained with
di(2-ethylhexyl)amine optionally combined with polyoxyethylene (15)
octadecylamine (available as Ethomeen C/25 from Armak Chemicals Division
of Akzo Chemie America).
Ranges and amounts of ingredients: Each of the above-named components is
included in the water-coagulable coating compositions as follows:
______________________________________
Urethane resin(s)
Up to 48%
Nonionic surfactant(s)
Up to 8%
Water Up to 6%
Antimicrobial Up to 4%
Water-miscible polar
Balance
organic solvent
______________________________________
It will be understood that the coating composition may contain any of the
usual coating additives and adjuvants, such as a pigment or colorant,
water repellent, antistat, etc. The quantities of each of these
ingredients may be varied depending upon the result desired, for instance
depending on the coating viscosity and total solids requirements. Each of
the above-listed ingredients must be present in the minimum amount
indicated or, if an optional ingredient, must be present in an amount of
at least 0.1%. All parts and percentages herein are expressed by weight
unless otherwise indicated.
Performance requirements for urethane-coated fabrics will vary depending
upon the application or end use to which the fabric is exposed. As a point
of reference, and without particular limitation, a typical urethane-coated
nylon taffeta for use in constructing rainwear will have the following
minimum values:
______________________________________
Moisture vapor transmission rate
800 (ASTM E-96A)
(g/m.sup.2 /24 hours)
Hydrostatic pressure resistance (psi)
10
Coating weight (oz/yd.sup.2)
0.3
______________________________________
The coating formulation was prepared as follows: the urethane resin or
mixture of resins is preweighed into a container. Water, the polar organic
solvent, usually DMF, the surfactant, and the antimicrobial are preweighed
into a separate container and mixed thoroughly. The water/solvent mixture
is then added to the urethane under agitation. Care is taken not to mix
the antimicrobial in its methanol solution with the urethane prior to
diluting the antimicrobial with the polar solvent (DMF), otherwise
coagulation is expected to occur. The optimum procedure for mixing of
ingredients and order of mixing will be determined through a brief series
of small-scale experiments, care being taken to avoid premature
coagulation of the coating solution.
Once the coating solution is prepared, the urethane coating is applied to
any textile substrate capable of supporting the liquid film by any
conventional coating method as is appropriate for use in the wet
coagulation method. The coated fabric is then dipped in a coagulation bath
consisting of water, or water and an additive to alter coagulation rate,
e.g. DMF; surfactant, etc. During the coagulation step the majority of the
DMF in the DMF/urethane film migrates into the coagulation bath and is
replaced by water, generating a microporous, spongy film on the fabric
surface. After additional washing to remove all the DMF, the fabric is
dried and given an optional water repellent finish.
The process is illustrated in more detail in FIG. 1 in which the fabric 1
to be coated is taken from a fabric supply 2, and passed, via a series of
feed rolls 3, to a knife-over-roll coater 4 which applies the coating
solution from a supply tank (not shown). The coated fabric is then led in
the "wet" condition to a coagulation tank 5 filled with water 6 or
water-enhanced liquid where a major portion of the DMF is replaced with
water leaving a coherent, tenacious, spongy, microporous film 7 on the
fabric. The coated fabric is squeezed through a set of rolls 8, then led
to a saturator 9 filled with water to remove additional quantities of DMF,
then skyed and accumulated at 10, directed to a series of wash boxes 11
where the coated fabric is washed with water, then squeezed through a pair
of rollers 12 (not shown) and dried. Arrangements consistent with the wet
coagulation technique in addition to that depicted in FIG. 1 may be used.
EXAMPLE
A coating mixture was prepared containing two urethane resins, a nonionic
surfactant and other diluents according to the mixing instructions given
above and having the following formulation:
______________________________________
amount (wt %)
______________________________________
urethane resin 29.7
(Texthane 620-C)
urethane resin 25.4
(Texthane 420-C)
nonionic surfactant
2.0
(Pluronic L-35)
DMF 40.9
water 2.0
______________________________________
Total solids was 19.8%. To this solution various amounts of the bioactive
silyl quaternary ammonium compound was added ranging from none (sample H)
and from 0.2% to 0.6% (samples A through F) calculated on the weight of
the overall solution. In addition, an afterfinish of 0.4% of the bioactive
silyl quaternary ammonium was applied to samples also containing the
bioactive compound in the urethane coating (D,E,F) and to a sample with no
bioactive compound in the finish (G). The solutions and finishes were
coated onto a 100% polyester woven fabric. For purposes of comparison two
commercially available vapor-permeable, water-repellent fabrics, Entrant
and GoreTex, were evaluated.
All samples were evaluated for bacterial reduction and mildew coverage
measured according to Dow Corning Corporate Test Method 0923 and modified
A.A.T.C.C. Test Method 30 procedures, respectively, and the results were
as follows:
__________________________________________________________________________
% Bioactive % Bioactive
% Bacterial
cpd in cpd in Reduction
% Mildew Coverage
Sample
Coating
Finish Original
10 MW*
Original
10 MW*
__________________________________________________________________________
A 0.2 -- 58.8 0 30 30
B 0.4 -- 62.7 1.6 10 20
C 0.6 -- 97.4 100 0 10
D 0.2 0.4 100 0 10 10
E 0.4 0.4 100 4.7 10 10
F 0.6 0.4 99.9+
3.3 10 10
G -- 0.4 99.9 0 90 75
H -- -- 0 90
Entrant 0 90
Goretex 0 90
__________________________________________________________________________
*machine washings
The results show that the % bacterial reduction is quite high on the
original (unlaundered) samples. After ten machine washings (MW), the %
bacterial reduction is generally low, but bacterial growth is prevented.
That is, the coated fabric has bacteriostatic properties. In sample F
(0.6% of bioactive compound in the coating), there was 100% reduction of
bacteria; that is, the sample had bacteriocidal properties. In general,
the treatments also reduced the growth of mildew substantially in
comparison with untreated fabric, Gore-Tex or Entrant.
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